HAZOP (Hazard and Operability Study) in ISO 26262
14 chapters HAZOP forces you to think in deviations, not just failures. By applying a disciplined set of guide words to each design intention, this method systematically surfaces the hazards a checklist would never find and feeds them straight into the ISO 26262 hazard analysis and risk assessment.
How You Learn
Video and text stay in sync. As you scroll through the chapter, the video jumps to the matching explanation automatically.
Learning Objectives
Think in deviations, not failures
Anchor every analysis on a design intention and use guide words to systematically negate and distort it.
Apply the eleven guide words
Generate value, functional, timing, and sequence deviations for any parameter or signal.
Run a four-phase HAZOP study
Move from definition and preparation through a facilitated examination to documented follow-up.
Extend HAZOP to software and data
Examine signals, messages, and data for frozen, stale, corrupted, and out-of-order deviations.
Chapters
Why HAZOP - Thinking in Deviations
Why disciplined deviation thinking finds hazards that failure-first methods and checklists systematically miss.
Origins & Philosophy - Intention vs Deviation
How a process-industry technique became a structured way to challenge every stated design intention.
Guide Words - The Engine of HAZOP
The eleven guide words (NO, MORE, LESS, AS WELL AS, PART OF, REVERSE, OTHER THAN, EARLY, LATE, BEFORE, AFTER) that turn a parameter into a deviation.
HAZOP Inside ISO 26262
How HAZOP findings feed the hazard analysis and risk assessment, driving safety goals and ASIL assignment.
The HAZOP Worksheet
The standard worksheet that records element, guide word, deviation, causes, consequences, safeguards, and recommendations.
The Four Phases
The full study lifecycle of definition, preparation, examination, and documentation with follow-up.
Definition & Preparation
Scoping the study, choosing nodes and parameters, and assembling the design intention before the team meets.
The Examination Session
How a facilitated session systematically walks each element and guide word to expose and record deviations.
HAZOP for Software, Signals & Data
Extending guide words to signals, messages, and data so software behaviour is examined as rigorously as physical flow.
Worked Example - Value & Functional Deviations
A full HAZOP of electric power steering assist torque, exploring MORE, LESS, NO, and REVERSE assist deviations.
Worked Example - Timing & Sequence Deviations
A HAZOP of an AEB decision chain where deviations are invisible to value checks but still cause collisions.
Documentation, Follow-up & Integration
Turning worksheet findings into tracked actions and integrating them into the wider ISO 26262 safety lifecycle.
Strengths, Limits & Method Comparison
Where HAZOP is strong on interaction hazards and how it compares with FMEA, FTA, and STPA.
Pitfalls, Best Practices & Facilitation
The facilitation habits and common traps that separate a rigorous HAZOP from a box-ticking exercise.
Diagrams & Visuals
Guide-Word Deviation Matrix
Maps each guide word against a parameter to generate the full grid of candidate deviations for an element.
Intention-to-Deviation Flow
Shows how a stated design intention is negated or distorted into a hazardous deviation.
Four-Phase Study Lifecycle
Traces a HAZOP from definition and preparation through examination to documentation and follow-up.
HAZOP-to-HARA Integration Map
Follows a worksheet deviation as it becomes a hazardous event, safety goal, and ASIL assignment.
EPS Torque Deviation Worksheet
Visualises the value and functional deviations of steering assist torque from the worked example.
AEB Timing Window Diagram
Illustrates how early and late braking decisions fall outside the supervised latency window.
Timing HAZOP of an Automatic Emergency Braking Decision Chain
Applying EARLY, LATE, BEFORE, and AFTER to an AEB decision chain reveals deviations that value checks cannot see: a brake command can be perfectly correct and still arrive too late to avoid the collision. Each deviation is measured against a tight latency budget and its supervised window before consequences and safeguards are recorded.
- LATE braking: correct decision arrives after the last point where the crash is avoidable
- EARLY braking: the system brakes hard for no target, risking a rear-end collision
- Sequence deviation: a target frame processed out of order corrupts the decision
- Timing deviations proven invisible to any value-based plausibility check
- Latency budget assessed against a supervised watchdog window
- Consequences, safeguards, and recommendations captured per worksheet row
AEB Timing HAZOP Worksheet
Master HAZOP and Feed Your ISO 26262 HARA
Work through the guide-word engine, the four phases, and two full worked examples to surface deviations a checklist would never catch.
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